Recently, as wireless communication devices such as smart phones are rapidly developed, various kinds of ICs, for example, BGA ICs having 200 or more lead balls and a 0.4 mm or less pitch, are developed and produced, and such ICs are required to be adapted for mass production.
Generally, ICs, the leads of which are arranged on a perimeter of an IC in two rows, for example, as shown in FIG. 1, a BGA IC 1 that has 280 balls 2 and 0.4 mm lead pitch, are mainly produced.
In the following description, the same reference numerals are used throughout the different drawings to designate the same or similar components, and designation of the same reference numerals will be omitted in some drawings.
As shown in FIGS. 2 and 3, to test an IC 1, a conventional IC test method includes electrically connecting lead balls 2 of an IC to respective upper pins 13 of spring contacts of a socket 15, and electrically connecting lower pins of socket contacts to a PCB 16.
An important point of the conventional IC test method is that the socket device must be able to repeatedly test ICs with lead balls having a diameter of 0.25 mm tens of thousands of times. Here, the socket device generally includes the PCB 16, the socket 15, a socket guide 17, an IC insert 20 and an IC pusher 23. Ultimately, it is very significant that the upper pins 13 of the socket contacts must be reliably connected to the corresponding IC balls mechanically and electrically.
More precisely, a test is conducted, after the IC balls 2 of the IC are disposed on the respective upper pins 13 of the socket contact without being displaced from the correct positions and the IC is pushed until the upper pins 13 of the contacts that have been in contact with the respective IC balls are compressed by 0.3 mm to make electrical connection reliable.
Problems that have occurred in the conventional IC test method for many years are derived from the fact that the IC balls 2 of the IC must be precisely disposed on the respective upper pins 13 of the socket contact without being displaced from the correct positions. The reason of occurrence of these problems is because dimension tolerances of components and machining accumulated tolerances make it difficult to precisely dispose the IC balls 2 of the IC on the respective upper pins 13 of the socket contact without being displaced from the correct positions when components are assembled with each other. The above problems may induce damage, deformation or breakage, particularly, of the upper pins 13 of the socket contacts. In this case, the damaged or deformed upper pins may come into contact with the bottom of the IC or other neighboring balls of the IC, thus resulting in damage to the IC or a reduction of a test yield rate.
In more detail, the dimension of an IC with dimensional tolerance is 14.00+/−0.10 mm×16.5+/−0.10 mm. That is, although the length of the IC is 16.5 mm, it is allowed if it is within a range from 16.40 mm to 16.60 mm. The outer diameter of each ball is 0.25+/−0.05 mm. This means that the outer diameter of the ball ranges from 0.20 mm to 0.30 mm. As shown in FIGS. 2 and 3, an insert 20 that is one of the components of a device for testing an IC functions to receive the IC. The insert 20 is manufactured with a machining tolerance of +0.02 mm/−0.00 mm such that a distance between two IC guide surfaces 22 of the insert 20 that face each other typically becomes a length that a margin length 0.02 mm is added to 16.6 mm that is the maximum length of the IC. Therefore, the maximum distance between the IC guide surfaces 22 of the insert 20 becomes 16.64 mm. If an IC having a length of 16.40 mm that is the minimum length of the IC is received into the insert 20, a clearance of 0.24 mm (16.64 mm−16.40 mm) occurs. If the IC is placed such that one side thereof is brought into close contact with one guide surface of the insert 20, the IC is displaced from the center of the insert 20 by 0.12 mm. Moreover, in an assembly between the insert 20 and the socket guide 17, a positional tolerance and an assembly tolerance between an insert position guide hole 21 of the insert and an insert position guide pin 19 of the socket guide are added. Also, in an assembly between the socket guide 17 and the socket, a positional tolerance and an assembly tolerance between a socket position guide pin 18 of the socket guide 17 and a socket position guide hole 14 of the socket are added. Thus, the IC that has been displaced from the center of the IC by 0.12 mm may be further displaced therefrom by 0.03 mm or more. As a result, the balls of the IC may be displaced from the correct positions of the centers of the upper pins of the corresponding socket contacts by 0.15 mm or more.
In brief, the IC balls 2 that must be placed at the correct positions on the centers of the upper pins 13 of the respective socket contacts and be electrically connected to upper pins 13 may be displaced from the correct positions by 0.15 mm or more. In the case where the diameter of each ball is 0.20 mm, the outer edge of the ball may be displaced from the center of the upper pin of the corresponding socket contact by 0.05 mm.
FIG. 4 illustrates a normal state in which the lead balls 2 of the IC are precisely disposed at correct positions on the upper pins 13 of the corresponding socket contacts. FIG. 5 illustrates an abnormal state in which the lead balls of the IC are displaced to the left by a distance of d″ from the correct positions of the upper pins of the socket contacts. In the case of FIG. 5, abnormal electrical contact is caused. Furthermore, the upper pins 13 of the socket contacts may be bent or broken. As such, a problem of an IC being damaged or a defective test being caused may occur. This problem is one of several significant problems that must be solved in an IC test. Such conventional problems will become more problematic if ICs with lead balls having a narrow pitch of 0.4 mm, 0.35 mm, 0.30 mm, etc. are mainly produced. Therefore, improvement countermeasures to solve the conventional problems in the IC test are required.